drm: mali-dp: Disable planes when their CRTC gets disabled.

Make sure only the planes on the active CRTCs get committed and
that all planes on the disabled CRTCs get turned off.

Reviewed-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>